Many integrated-circuit devices, such as memory devices, include function circuits that can be selected to perform predetermined functions or provide predetermined design options. For example, a memory device may include substitution circuits that, when enabled, replace defective matrix memory columns with redundant memory columns. If, during initial testing of the memory device, a matrix column is found to be defective, a substitution circuit corresponding to or including a redundant memory column is selected to perform the replacement. Typically, such a replacement is transparent to the circuitry external to the memory device, and entails disabling the defective matrix memory column and routing data to the redundant memory column whenever the external address signal selects the defective column.
Because such integrated circuit devices often include a predetermined number of function circuits, each function circuit is associated with or includes an enable circuit that is programmed to enable the function circuit if it is selected, or is left unprogrammed if the function circuit is not selected. One reason such integrated circuit devices include a predetermined number of function circuits is that the need for repair-type circuits (such as the above-discussed substitution circuits) often cannot be determined until after the integrated circuit device has been manufactured. Another reason is that the mask rework and other changes required to alter the number of function circuits from batch to batch may significantly increase the cost and complexity of the manufacturing process. Thus, the programmable enable circuits allow the memory device to select and activate only the needed function circuits.
A problem with existing programmable enable circuits, such as disclosed in U.S. Pat. No. 5,345,110 to Renfro et at., is that in the programmed or unprogrammed state, they often conduct a standby or quiescent current, i.e., dissipate power at times other than while their components are switching. The sum of the standby currents of all of the enable circuits in the integrated circuit device often generates additional heat in the integrated circuit device and increases the power that the integrated circuit device requires.
An existing enable circuit that is responsive to an activation signal, which is typically generated elsewhere on the integrated circuit device, only conducts a standby current when it is in a programmed state and the activation signal is present at its input. Standby current in such a circuit has been reduced by pulsing the activation signal. However, such pulsing often requires additional circuitry on the integrated circuit device and does not eliminate the enable circuit's quiescent power dissipation.